Water-glycol hydraulic fluid composition and supplementary additive therefor

ABSTRACT

The present invention provides a water-glycol hydraulic fluid composition comprising an alkanolamine compound according to the general formula (1), wherein the water-glycol hydraulic fluid composition comprises 20-60% by mass water, 20-60% by mass glycol, 0.6-1.2% by mass fatty acid lubricant, and 0.01-0.06% by mass alkaline hydroxide compound selected from potassium hydroxide and/or sodium hydroxide, and has an alkali reserve of 10-25, wherein R 1  and R 2  are hydrocarbon groups having from 1 to 8 carbon atoms, and R 3  is a hydrocarbon group having 2 or more carbon atoms.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a water-glycol hydraulic fluid composition and a supplementary additive therefor.

BACKGROUND OF THE INVENTION

The hydraulic fluid is used as a medium for transmitting power in hydraulic equipment. Petroleum-based hydraulic fluids are widely used, and commonly used general hydraulic fluids use a mineral oil-based base oil such as a highly refined paraffin-based base oil.

However, because hydraulic equipment, aluminum die casting machines, and extrusion machines used in, for example, steelworks operate at high temperatures and under high pressure, there is a high risk of fire. In order to avoid the risk of fire, a water-glycol hydraulic fluid is used as the hydraulic fluid in this equipment instead of a hydraulic fluid using a mineral oil as a base oil.

When a water-based hydraulic fluid is used, rust prevention is required so that hydraulic operations can be performed smoothly and the service life of hydraulic equipment can be extended. In particular, a volatile, alkaline rust inhibitor must be added so that wall surfaces and ceiling surfaces not in contact with the hydraulic fluid do not rust. Also, while water-glycol hydraulic fluids have excellent performance, their performance deteriorates during use due to a drop in pH and oxidation. Therefore, water-based hydraulic fluid compositions obtained by, for example, adding a polyoxyalkylene glycol diether compound having a specific structure, a polyoxyalkylene glycol monoether compound, a polyoxypropylene glycol monoether compound, and a fatty acid salt to water are used to improve performance in terms of pH drop suppression and oxidation stability, for example in JP 3233490 B2.

Water-glycol hydraulic fluids contain water and glycol as main components, but a phenomenon occurs in hydraulic equipment using these hydraulic fluids in which the water of these hydraulic fluids is vaporized during use. A liquid phase or vapor phase rust inhibitor is generally used as an additive in a water-glycol hydraulic fluid, but this additive is vaporized along with the water during use and so the properties of the water-glycol hydraulic fluid may exceed their appropriate range.

In this case, it is common practice to add a supplementary additive to maintain the performance of water-glycol hydraulic fluids and keep the properties of hydraulic fluids within the appropriate range.

Therefore, it is an object of the present invention to improve the performance of water-glycol hydraulic fluids used in hydraulic equipment and to obtain a supplementary additive that can effectively maintain vapor phase rust prevention performance.

SUMMARY OF THE INVENTION

The present invention provides a water-glycol hydraulic fluid containing 20-60% by mass water and 20-60% by mass glycol, with the remainder being, for example, a fatty acid-based lubricant, alkaline hydroxide compound, thickener, anticorrosive, and antifoaming agent to bring the total to 100% by mass. As a result of extensive research conducted to solve this problem, the present inventor and others discovered that use of a specific alkanolamine compound could significantly improve the vapor phase rust prevention properties of a water-glycol hydraulic fluid, and that this alkanolamine compound could be used as an effective supplementary additive.

In the present invention, an alkanolamine compound represented by the general formula below is blended into a water-glycol hydraulic fluid.

In the general formula, R₁ and R₂ are hydrocarbon groups having from 1 to 8 carbon atoms, and R₃ is a hydrocarbon group having 2 or more carbon atoms. This alkanolamine compound is also used as a supplementary additive in a water-glycol hydraulic fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram used to explain the device used to perform the vapor phase rust prevention test in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, a water-glycol hydraulic fluid with excellent rust prevention properties can be obtained by adding a specific alkanolamine compound. In addition, when the water in a water-glycol hydraulic fluid being used in hydraulic equipment is vaporized and this alkanolamine compound is used as a supplementary additive, the vapor phase rust prevention properties of a water-glycol-based working liquid, which decline with the vaporization of water, can be restored to the initial level of performance.

The alkanolamine compound of the present invention is represented by the following general formula (1).

Here, R₁ and R₂ represent hydrocarbon groups having from 1 to 8 carbon atoms, preferably 1-4 carbon atoms, and more preferably 3 or 4 carbon atoms. R₁ and R₂ may have the same number of carbon atoms or a different number of carbon atoms. However, the same number of carbon atoms is usually preferred. R₃ is a hydrocarbon group having 2 or more carbon atoms. However, because the water solubility of a compound tends to decrease as the number of carbon atoms increases, 2-4 carbon atoms are preferred.

Examples of these alkanolamine compounds include N,N-dimethylaminoethanol, N,N-diethylaminoethanol, N,N-dipropylaminoethanol, N,N-dibutylaminoethanol, N,N-dipentylaminoethanol, N,N-dihexylaminoethanol, N,N-diheptylaminoethanol, N,N-dioctylaminoethanol, N,N-dimethylaminopropanol, N,N-diethylaminopropanol, N,N-dipropylaminopropanol, N,N-dibutylaminopropanol, N,N-dipentylaminopropanol, N,N-dihexylaminopropanol, N,N-diheptylaminopropanol, N,N-dioctylaminopropanol, N,N-dimethylaminobutanol, N,N-diethylaminobutanol, N,N-dipropylaminobutanol, N,N-dibutylaminobutanol, N,N-dipentylaminobutanol, N,N-dihexylaminobutanol, N,N-diheptylaminobutanol, N,N-dioctylaminobutanol, N-butyl (N-pentyl) aminoethanol, N-butyl (N-hexyl) amino ethanol, N-butyl (N-heptyl) aminoethanol, N-butyl (N-pentyl) aminopropanol, N-butyl (N-hexyl) aminopropanol, and N-butyl (N-heptyl) aminopropanol. These alkanolamine compounds are added so that the alkali reserve of the water-glycol hydraulic fluid as specified in JIS K2234-1994 is from 10 to 25, preferably from 15 to 23, and more preferably from 18 to 21. The 20° C. density of these alkanolamine compounds is preferably from 0.86 to 0.89. When the density exceeds 0.89, volatility is reduced and the vapor phase rust prevention properties decline relative to the alkali reserve.

These alkanolamine compounds are used in water-glycol hydraulic fluid, and there are no particular restrictions on the composition of the water-glycol hydraulic fluid. However, the following composition is preferred. Relative to a total of 100% by mass, water is 20-60% by mass, preferably 30-50% by mass, a fatty acid-based lubricant is 0.6-1.2% by mass, an alkali hydroxide compound is 0.01-0.12% by mass, and a glycol is 20-60% by mass.

Examples of glycols include ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, dibutylene glycol, dihexylene glycol, trimethylene glycol, triethylene glycol, and tripropylene glycol. These glycols can be used alone or in mixtures of two or more. Use of propylene glycol or dipropylene glycol is preferred. The amount of glycol used is 20-60% by mass, and more preferably 30-50% by mass, relative to the total mass of the water-glycol hydraulic fluid composition.

Examples of fatty acid-based lubricants include saturated fatty acids such as capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid and stearic acid, and unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid. Sodium salts of these fatty acids can also be used. Examples include sodium caprate, sodium undecylenate, sodium laurate, sodium tridecylenate, sodium myristate, sodium pentadecylate, sodium palmitate, sodium margarate, sodium stearate, sodium oleate, sodium linoleate, and sodium linolenate.

There are also aromatic fatty acids and dimerized fatty acids. Dimerized fatty acids are liquid fatty acids containing a dibasic acid of a C36 dicarboxylic acid produced by dimerization of a C18 unsaturated fatty acid containing a vegetable fat or oil as a main component, but also a monobasic acid and a tribasic acid. These fatty acids, sodium salts of fatty acids, and dimerized fatty acids may be used alone or in mixtures of two or more as the fatty acid-based lubricant.

Examples of alkali hydroxide compounds include potassium hydroxide and sodium hydroxide. These may be used alone or together when appropriate. The amount of alkaline hydroxide compound is 0.01-0.12% by mass, and more preferably 0.04-0.06% by mass, relative to the total mass of the composition.

A specific phosphoric acid ester compound can be used as an antiwear agent. This phosphoric acid ester has the following structure.

In this formula, R₄ and R₅ may be the same or different and represent a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms, R₆ represents a hydrocarbon group having from 1 to 20 carbon atoms, R₇ represents a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms, and X₁, X₂, X₃ and X₄ may be the same or different and represent an oxygen atom or a sulfur atom.

If necessary, commonly used additives may be included in the water-glycol hydraulic fluid. Examples include thickeners, lubricants, metal deactivators, wear inhibitors, extreme pressure agents, dispersants, metal detergents, friction modifiers, corrosion inhibitors, anti-emulsifiers, and defoamers. These additives may be used alone or in combination with each other. Here, an additive package for water-glycol hydraulic fluids may be used.

An alkanolamine compound described above can be used as a supplementary additive while a water-glycol hydraulic fluid is being used. When a new water-glycol hydraulic fluid is used, the water is vaporized, additives are vaporized along with the water, and the vapor phase rust prevention properties decline. One way of determining the vapor phase rust prevention properties of a water-glycol hydraulic fluid is to measure the alkali reserve as specified in JIS K2234-1994. Here, an alkanolamine compound described above is added to a water-glycol hydraulic fluid as a supplementary additive until the initial alkali reserve has been restored. When vapor phase rust prevention properties are maintained, a water-glycol hydraulic fluid can be used stably over a long period of time.

Among the alkanolamine compounds listed above, dimethylethanolamine and diethylethanolamine have been designated as toxic substances, so strict controls are required when handling them. Therefore, when used as a supplementary additive, R₁ and R₂ most preferably are 3 or 4 carbon atoms. This makes handling of the supplementary additive easy, and the hydraulic fluid in hydraulic equipment can be safely replenished by an on-site worker.

EXAMPLES

Water-glycol hydraulic fluids containing an alkanolamine compound of the present invention will now be described in detail with reference to the following non-limiting examples and comparative examples.

The “alkali reserve” mentioned above is determined by measuring the basic components in a water-glycol hydraulic fluid using the alkali reserve measuring method specified in JIS K2234-1994. The alkali reserve indicates the amount of 0.1N hydrochloric acid in ml required to adjust the pH to 5.5 and neutralize the basic components in 10 ml of a sample oil.

Example 1

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 1.90% by mass N,N-dibutylaminoethanol as the alkanolamine compound, 37.73% by mass propylene glycol as the glycol, 16.10% by mass water-soluble polymer as the thickener, identical amounts of dimerized fatty acid and lauric acid as the fatty acid lubricants for a total of 0.80% by mass, 0.06% by mass sodium hydroxide as the alkali hydroxide compound, 1.57% by mass other additives such as a corrosion inhibitor and defoamer, and 41.84% by mass water. The alkali reserve obtained in accordance with JIS K2234-1994 was 20. The 40° C. kinematic viscosity was 46 mm²/s and the pH was 11. The N,N-dibutylaminoethanol used here had a molecular weight of 173, a 20° C. density of 0.860, a flash point of 90° C., and a boiling point of 226° C.

Example 2

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 1.00% by mass of N,N-dimethylaminoethanol as the alkanolamine compound, 38.63% by mass glycol, 16.10% by mass thickener, 0.80% by mass fatty acid lubricant, 0.06% by mass alkaline hydroxide compound, 1.57% by mass other additives, and 41.84% by mass water. The alkali reserve obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm²/s. The N,N-dimethylaminoethanol used here had a molecular weight of 89, a 20° C. density of 0.888, a flash point of 40° C., and a boiling point of 134° C.

Comparative Example 1

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 1.40% by mass of N-ethyldiethanolamine as the alkanolamine compound, 38.63% by mass glycol, 16.10% by mass thickener, 0.80% by mass fatty acid lubricant, 0.06% by mass alkaline hydroxide compound, 1.57% by mass other additives, and 41.84% by mass water. The alkali reserve obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm²/s. The N-ethyldiethanolamine used here had a molecular weight of 133, a 20° C. density of 1.07, a flash point of 124° C., and a boiling point of 251° C.

Comparative Example 2

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 1.00% by mass of N-methylethanolamine as the alkanolamine compound, 38.63% by mass glycol, 16.10% by mass thickener, 0.80% by mass fatty acid lubricant, 0.06% by mass alkaline hydroxide compound, 1.57% by mass other additives, and 41.84% by mass water. The alkali reserve obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm²/s. The N-ethyldiethanolamine used here had a molecular weight of 75, a 20° C. density of 0.940, a flash point of 73° C., and a boiling point of 156° C.

Comparative Example 3

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 1.00% by mass of 2-ethylaminoethanol as the alkanolamine compound, 38.23% by mass glycol, 16.10% by mass thickener, 0.80% by mass fatty acid lubricant, 0.06% by mass alkaline hydroxide compound, 1.57% by mass other additives, and 41.84% by mass water. The alkali reserve obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm²/s. The 2-ethyldiaminoethanol used here had a molecular weight of 117, a 20° C. density of 0.918, a flash point of 77° C., and a boiling point of 199° C.

Comparative Example 4

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 1.23% by mass of mono-n-butylethanolamine as the alkanolamine compound, 38.40% by mass glycol, 16.10% by mass thickener, 0.80% by mass fatty acid lubricant, 0.06% by mass alkaline hydroxide compound, 1.57% by mass other additives, and 41.84% by mass water. The alkali reserve obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm²/s. The N-mono-n-butylethanolamine amine used here had a molecular weight of 117, a 20° C. density of 0.893, a flash point of 77° C., and a boiling point of 199° C.

Comparative Example 5

A water-glycol hydraulic fluid was obtained by thoroughly mixing together 39.63% by mass glycol, 16.10% by mass thickener, 0.80% by mass fatty acid lubricant, 0.06% by mass alkaline hydroxide compound, 1.57% by mass other additives, and 41.84% by mass water. Because an alkanolamine compound was not included the alkali reserve obtained in accordance with JIS K2234-1994 was 9, and the 40° C. kinematic viscosity was 46 mm²/s.

Tests

The vapor phase rust prevention properties of the examples and comparative examples were evaluated as follows.

Vapor Phase Rust Prevention Test

As shown in FIG. 1 , 100 g of the water-glycol hydraulic fluid in an example or a comparative example was added to a hard glass test tube with a height of 600 mm and an outer diameter of 50 mm used in the turbine oil oxidation stability test in JIS K2514-2, and two 80×30×2 mm test pieces of rolled steel for general structures (SS-400) were suspended above and below the test tube. The opening at the top of the test tube was covered with a cooler, the bottom of the test tube was placed in a constant temperature bath at 50° C., and the presence or absence of rust on the test pieces was visually confirmed after allowing the tube to stand for 200 hours.

Evaluation Standards:

Rust was observed on neither test piece Passed Rust was observed on one or both test pieces . . . Failed

The test results are shown in Table 1. In Example 1 and Example 2 shown in Table 1, an alkanolamine compound was included so that the alkali reserve was 20.0. No rust was observed in the vapor phase rust prevention test performed on either example, and both obtained passing results.

TABLE 1 Ex. 1 Ex. 2 N,N-Dibutylaminoethanol 1.90 N,N-Dimethylaminoethanol 1.00 Glycol 37.73 38.63 Thickener 16.10 16.10 Fatty acid lubricant 0.80 0.80 Alkali hydroxide compound 0.06 0.06 Other additives 1.57 1.57 Water 41.84 41.84 Alkali reserve 20.0 20.0 Vapor phase rust prevention test Passed Passed

In Comparative Example 5 shown in Table 2, an alkanolamine compound was not included so the alkali reserve was a low 9.0, rust was observed in the vapor phase rust prevention test, and a failing result was obtained. In Comparative Example 2 to Comparative Example 4, an alkanolamine compound was included so that the alkali reserve was 20.0, but the alkanolamine compounds were not a dialkylaminoalkanol according to the present invention, so rust was observed in the vapor phase rust prevention test, and failing results were obtained.

TABLE 2 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 N-Ethyldiethanolamine 1.40 N-Methylethanolamine 1.00 2-Ethylaminoethanol 1.00 Mono-n- 1.23 butylethanolamine Glycol 38.23 38.63 38.63 38.40 39.63 Thickener 16.10 16.10 16.10 16.10 16.10 Fatty acid lubricant 0.80 0.80 0.80 0.80 0.80 Alkali hydroxide 0.06 0.06 0.06 0.06 0.06 compound Other additives 1.57 1.57 1.57 1.57 1.57 Water 41.84 41.84 41.84 41.84 41.84 Alkali reserve 20.0 20.0 20.0 20.0 9.0 Vapor phase rust Failed Failed Failed Failed Failed prevention test 

1. A water-glycol hydraulic fluid composition comprising an alkanolamine compound according to the general formula (1), wherein the water-glycol hydraulic fluid composition comprises 20-60% by mass water, 20-60% by mass glycol, 0.6-1.2% by mass fatty acid lubricant, and 0.01-0.06% by mass alkaline hydroxide compound selected from potassium hydroxide and/or sodium hydroxide, and has an alkali reserve of 10-25,

wherein R1 and R2 are hydrocarbon groups having from 1 to 8 carbon atoms, and R3 is a hydrocarbon group having 2 or more carbon atoms.
 2. A water-glycol hydraulic fluid composition according to claim 1, wherein the alkanolamin according to general formula (1) is N,N-dibutylaminoethanol.
 3. A method for adjusting the alkali reserve of a water-glycol hydraulic fluid composition, said method comprising the addition of a supplementary additive comprising a alkanolamine of general formula (1) to the water-glycol hydraulic fluid to adjust the alkali reserve of the water-glycol hydraulic fluid composition to 10-25 during use

wherein R1 and R2 are hydrocarbon groups having from 1 to 8 carbon atoms, and R3 is a hydrocarbon group having 2 or more carbon atoms.
 4. A method according to claim 3, wherein the alkanolamine is N,N-dibutylaminoethanol 